cmd= see description
[See also scroll down which shares this code and is distingished by having only one parameter and having the first parameter != 0]
This sequence is used with mouse highlight mode to communicate the selection start and allowed rows.
cmd is 0 then the highlighting is aborted and the terminal uses non highlighting mouse handling as in mouse down+up tracking.
cmd is non-zero then
start-row specify the selection start and
first-row specifies the first allowed row for the selection and
last-row specifies the first row that the selection may not enter into.